Plastic netting for wrapping articles

ABSTRACT

A biaxially-oriented plastic netting for use in wrapping articles includes diamond-shaped apertures formed by strands of the netting located at an acute angle to the longitudinal direction in which the web is tensioned for wrapping articles. Strips or strands of edge material are disposed along each longitudinal edge of the netting, and these strips are stretchable to an elongation for permitting the strands in the longitudinally extending central region of the netting to realign into a taught condition without substantial stretching. The strips or strands of edge material are sufficiently resistant to increasing elongation, after the strands in the longitudinally extending central region have become taut, to transmit tension forces to the strands along the longitudinally-extending edges of the netting, to thereby render the strands adjacent each longitudinal edge taut under the tension forces imparted to the netting when the netting is disposed in wrapping engagement with articles to be wrapped.

BACKGROUND OF THE INVENTION

The present invention relates generally to plastic netting for wrappingarticles, and more specifically to a particular form of plastic nettingfor use in wrapping palletized loads and other multiple package systems,with improved results.

The wrapping of palletized loads in order to unitize the load is wellknown. It is taught, for example, in U.S. Pat. Nos. 3,495,375; 3,867,806and 4,067,174, to utilize plastic films to wrap such loads.

The use of plastic netting for wrapping palletized loads also is knownin the art. The use of such netting is disclosed, for example, in U.S.Pat. Nos. 3,945,493 and 4,136,501 (Re. 31,191). The former patentteaches a process in which the net is heat shrunk about the load, whilethe latter patent teaches a process in which the net is stretched as itis being applied under tension. U.S. Pat. No. 4,206,846 relatesgenerally to similar subject matter for netting used in a palletwrapping operation.

U.S. Pat. Nos. 4,208,457 and 4,332,326, disclose the use of netting inwhich the strands are molecularly oriented before the net is applied tothe load.

U.S. Pat. No. 4,402,409 also is directed to improved netting for use ina pallet wrapping operation, in which the netting has a relatively lowdegree of permanent stretch and a relatively high degree of elasticstretch.

All of the plastic netting used to heretofore and referred to above inpallet wrapping operations has been of the "square mesh" configurationor "bias configuration". Although U.S. Pat. Nos. 4,332,326 and 4,402,409make reference to "diamond mesh" configuration netting, theyspecifically teach cutting the formed, tubular netting in a manner toconvert the netting into a "square mesh" net, before the net is used ina pallet wrapping operation.

The "square mesh" and the "bias configuration" nets of the prior artconsist of longitudinal and transverse strands arranged at substantiallyright angles to each other. When these nets are used in pallet wrappingoperations, the longitudinal strands, i.e., the strands extending in thedirection of wrap (typically the machine direction of web formation) arerequired to sustain most of the tension, due to the fact that thetension forces are imposed along the longitudinal direction in which themachine direction strands extend. The transverse strands actuallyprovide little or no support to the load. In fact, these transversestrands tend to buckle and become limp when the longitudinal strands aretensioned during a pallet wrapping operation. Thus, despite the factthat a load might be tightly wrapped by means of the tensioning of thelongitudinal strands, the relatively loose transverse strands tend topermit the load to shift to a degree which can be unacceptable. This isparticularly true when the transverse strands bridge a pair of articlesstacked upon each other on a pallet or other support structure.

U.S. Patent No. 4,741,442, covers an earlier invention by me, which, atthe time of filing, I believed to overcome the above-discusseddeficiencies of the "square mesh" and "bias configuration" netting.Specifically, in the '442 patent I described and claimed a plasticnetting for palletized loads, wherein diamond-shaped apertures wereformed by strands of the netting located at an acute angle to thelongitudinal direction in which the web was to be tensioned for wrappinga palletized load. It was believed that the strands defining thediamond-shaped apertures, by virtue of the fact that they were alldisposed at an acute angle to the tensioning direction, would becomeequally tensioned, along the entire extent of the net.

During subsequent experimentation I discovered that the nettingdescribed and claimed in the '442 patent actually had greaterdeficiencies than the prior art "square mesh" and "bias configuration"products. Specifically, the "diamond-shaped" netting forming the subjectmatter of the '442 patent had two significant problems, when used undertension as a wrap for a palletized load.

First, the netting necked-down excessively, i.e., to approximately20%-25% of its initial transverse dimension. Specifically, a nettinghaving an unstretched, transverse dimension of approximately 20 incheswas observed to neck-down to approximately 4 or 5 inches, under thetension forces normally applied to the netting during a pallet-wrappingoperation; e.g., 1-5 pounds force per inch of width.

Second, the sections of the netting adjacent the longitudinal edges werein a limp, floppy, untensioned condition under machine direction loadingof the type encountered in a pallet-wrapping operation. Although thelongitudinal center region of the netting did become taut, duepredominately to a shifting or change in alignment of the strands, asopposed to substantial stretching of the strands in that region, thestrands in the floppy end regions did not realign, and therefore wereincapable of contributing to any significant degree to preventing ashifting of a palletized load. Thus, contrary to the statements in myprior '442 patent, all strands of the diamond shaped netting were notsubjected to approximately equal tension when wrapped about a palletload.

In order to compensate for the inadequacy of the floppy ends toconstrain a palletized load, when employing the netting disclosed in the'442 patent, it would be necessary to provide a substantial degree ofoverlap between adjacent wraps of the netting, whereby floppy edges ofeach wrap would be covered by taut central sections of the adjacentwraps. Unfortunately, this results in the use of an excessive quantityof material, thereby resulting in undesired costs.

All of the patents referred to herein are incorporated by reference.Reference to these patents will disclose the wrapping methods used inpallet wrapping operations.

The U.S. Pat. No. 4,594,280 to Coyon et al., discloses an expandedperforated sheet having unexpanded sides 4. The structure is disclosedas being usable as an electrical resistance element, not as a flexibleweb of wrapping material.

The U.S. Pat. Nos. 3,040,968 to Long et al., 3,550,842 and 3,603,369,Scholz, and Bruno, 3,762,629, disclose wrappers provided with aperturedcentral regions surrounded by unapertured margins. There is nodisclosure of providing the edge regions with a different degree ofelasticity than the strand regions defining the apertures, for thepurpose of transmitting tension forces to the strands defining theapertures.

The U.S. Pat. No. 4,303,717, to Mercer, discloses a plastic nettinghaving apertures 7 and integrally formed selvedge 17. Mercer states thatthe stretch in the edge zone 17 is not substantially greater than thatof the zones between the immediately adjacent holes or depressions 7.There is no disclosure of forming the selvedge or edge zones 17 to bemore elastic than the strands defining the depressions 7, fortransmitting tension forces to said strands.

OBJECTS OF THE INVENTION

It is a general object of this invention to provide a plastic nettingfor use in wrapping articles, wherein virtually all of the strands inthe netting are maintained in a taut condition to cooperate in thearticle wrapping function.

It is a further object of this invention to provide a plastic nettingwhich can be used in a minimum quantity to provide a desired articlewrapping function.

It is a further object of this invention to provide a plastic nettingfor wrapping articles, such as palletized loads, wherein the individualstrands are maintained in a taut condition for providing a desiredarticle wrapping function.

It is a further object of this invention to provide a plastic nettingwhich can be tensioned about an article to be wrapped, without thenetting necking-down excessively in the transverse dimension.

SUMMARY OF THE INVENTION

The above and other objects of this invention are provided by abiaxially-oriented plastic netting for use in wrapping articles, saidnetting having diamond-shaped apertures formed by strands of the nettinglocated at an acute angle to the longitudinal direction in which the webis tensioned during a wrapping operation. The netting of this inventionincludes an edge material along each longitudinal edge thereof, and eachof the edge materials is stretchable to an elongation for permitting thestrands in the longitudinally extending central region of the netting torealign into a taut condition, without substantial stretching. The edgematerial, at said elongation, having sufficient resistance to anincrease in elongation to transmit tension forces along thelongitudinally extending edges and through the strands extending to saidedges, to thereby render the strands adjacent each longitudinal edgetaut under the tension forces imparted to the netting when disposed inwrapping engagement with articles to be wrapped.

In the preferred embodiment of this invention the plastic netting isemployed to wrap multiple articles which are stacked adjacent to, or ontop of each other, and most preferably to wrap palletized loads.

In accordance with this invention the edge material along thelongitudinal edges of the netting is stretched either below or beyondits elastic limit, under the tension forces imparted to the netting whenthe netting is in wrapping engagement with the articles to be wrapped.When the edge material is stretched beyond its elastic limit by wrappingof articles with the netting, most preferably the tension forcesimparted through the edge material to the strands attached theretoexceed the force imparted to the edge material at the elastic limit ofsaid edge material.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection the accompanying drawings, wherein:

FIG. 1 is a fragmentary isometric view of a diamond mesh net inaccordance with this invention; and

FIG. 2 is an end elevation view showing a typical palletized loadaccording to the present invention; being wrapped with the netting ofthis invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows, in fragmentary view, a continuous plastic netting 10 ofbiplanar diamond mesh configuration in which one set of strands 12overlies a second set of strands 14 and wherein both sets of strands aredisposed at an acute angle, alpha (α), to the machine direction of webformation, as is illustrated by the arrow 16.

In the preferred embodiment of this invention the strands are composedof a thermoplastic material which is extruded in accordance with knownprocedures to form the net 10 with the sets of strands 12 and 14 beingconnected at joints 18. Although the sets of strands 12 and 14 do extendgenerally in the longitudinal direction of net formation, as isillustrated by arrow 16, they are all disposed at an acute angle alpha(α) of less than 90 degrees to said longitudinal direction.Specifically, each of the sets of parallel strands 12 and 14 extendgenerally in the longitudinal direction, i.e., the direction of wrap,but at an angle alpha (α) of less than 90 degrees upwardly or downwardlywith respect to said longitudinal direction to provide two sets ofstrands which share tension applied to the netting 10 in thelongitudinal direction, at least in the central longitudinal regionthereof. Typically this longitudinal direction is also the machinedirection of web formation.

In accordance with this invention the netting is biaxially-oriented, andmost preferably is oriented within the range of 4:1-20:1, and mostpreferably in the range of 8:1-10:1. Typically, orientation will beaccomplished on staged drafter rolls in a normal manner, as is wellknown by those skilled in the art.

It also should be understood that although the preferred netting is ofthe biplanar arrangement shown in FIG. 1, it may be uniplanar of thetype produced in U.S. Pat. No. 2,919,467. However, the biplanarconfiguration, which also is described in the '467 patent, is the mostpreferred construction in accordance with this invention. The subjectmatter of the '467 patent is herein incorporated by reference.

Any of a wide variety of thermoplastic materials commonly used in themanufacturing of extruded netting may be utilized for the netting ofthis invention, provided that the material is capable of beingbiaxially-oriented, to thereby limit the ability of the individualstrands of the netting to stretch. Most preferably the material isbiaxially-oriented so that the individual strands of the netting, whenthe netting is in use under tension, will not thereafter stretch morethan 15%; preferably not more than 10% and most preferably less than 5%of the length of the tensioned strands.

Exemplary thermoplastic materials which may be usable in this inventionare polypropylene, blends of polypropylene and linear low densitypolyethylene, linear low density polyethylene, high densitypolyethylene, medium density polyethylene, polybutylene and blends andcopolymers thereof.

Referring specifically to FIG. 1, edge material 20, preferably in theform of strips or strands, are adhered to the plastic netting, alongeach of the longitudinal edges of said netting.

Unlike the biaxially-oriented plastic employed to form the nettingstrands 12 and 14, the edge material 20 must be stretchable (e.g.,elastic) to an elongation sufficient to permit the biaxially-orientedstrands 12 and 14 in the main body of the netting to shift or change inalignment, under the stresses imposed in the longitudinal direction ofthe netting during an article wrapping operation, to thereby cause themain body of the netting to become taut.

When the netting 10 is tensioned about the articles to be wrapped (e.g.articles 22 supported on a pallet 24--FIG. 2) the edge material 20thereof is stretched either below or beyond its elastic limit. If theedge material 20 is of the type which is stretched beyond its elasticlimit when tensioned about the articles to be wrapped, most preferablyit provides increasing resistance to increasing strain, beyond theelastic limit, to thereby transmit a force along the edge material andthe netting strands attached thereto, which is greater than the forceimparted to the edge material at the elastic limit thereof.

During wrapping of the netting about the articles to be wrapped, whichusually takes place under an applied force in the range of 1 and 5pounds of force per inch of width, the force transmitted through thestretched edge material 20 must be sufficient to prevent thelongitudinal edge regions of the netting from becoming floppy, and alsoto prevent an undesired degree of necking-down of the netting, in atransverse direction.

As stated above, edge materials within the scope of this invention areones which both exceed and which do not exceed their elastic limit whenstretched to a required elongation, for permitting the sets of strands12 and 14, at least in the central longitudinal region thereof, torealign into a taut condition. The important factor is that the edgematerial should be sufficiently resistant to increasing strain at therequired elongation, to transmit the necessary forces to the sets ofstrands 12 and 14 of the netting 10 along the longitudinal edges of thenetting, to maintain the netting taut in the regions along thelongitudinal edges thereof.

A number of different materials are believed to be usable in thisinvention to form the edge materials 20, including linear low densitypolyethylene, flexible polyvinyl chloride and thermoplastic elastomersor rubbers, such as Santoprene or Kraton. Polybutylene and polypropylenealso are possible candidates for use in the edge material. However, theplastics used to form the edge materials will not be biaxially-orientedto impair the stretchable characteristics thereof.

It is understood that the plastic netting 10 initially can be extrudedin the form of a tube, and that the edge material can be simultaneouslybonded to the tube, prior to forming the netting 10 by severing the tubemidway between the longitudinal edges of the edge material. In thismanner the tube is opened into a flat netting 10, with the strips ofedge material 20 along each longitudinal edge thereof.

It is also within the scope of this invention to coextrude the edgematerial along with the tubular netting; thereafter bond the coextrudededge material to the tubular netting and thereafter sever the tube alongthe center line of the coextruded edge material.

The specific method used to form the netting 10 is not considered to bea limitation on the present invention.

Without further elaboration the foregoing will so fully illustrate myinvention that others may, by applying current or future knowledge,adopt the same for use under various conditions of service.

I claim:
 1. A pallet load wrapped with at least one continuous length ofplastic netting, the length of plastic netting extending in alongitudinal direction and having one set of spaced substantiallyparallel strands extending at an angle of less than 90 degrees upwardlywith respect to the longitudinal direction and a second set of spacedsubstantially parallel strands overlying the first set and extending atan angle of less than 90 degrees downwardly with respect to thelongitudinal direction, said strands being joined at the intersectionsthereof and providing a diamond-like configuration to the netting, thenetting including longitudinally extending edges substantially parallelto the longitudinal direction of the netting, said netting beingbiaxially oriented to preclude substantial stretching of the strandsthereof under the tension forces applied in said longitudinal directionto wrap the pallet load with the netting, said one set of strands andsaid other set of strands being movable relative to each other under thetension forces applied in said longitudinal direction to permitelongation of the netting without substantial stretching of the strands,characterized in that an edge material extends along each longitudinaledge and is joined to both sets of strands, said edge materials beingstretchable to a greater extent than the strands in both sets of strandsunder the tension forces applied to the netting in the longitudinaldirection to wrap the pallet load, said tension forces being transmittedalong the stretched edge material and the strands of the netting joinedthereto so that substantially all of the netting strands, from onelongitudinal edge portion to the other longitudinal edge portion in adirection substantially transverse to said longitudinal direction aremaintained in a taut condition and under sufficient tension forimmobilizing the wrapped pallet load.
 2. The pallet load of claim 1wherein the edge material is stretched beyond its elastic limit underthe tension forces applied to the netting to wrap the pallet load. 3.The pallet load of claim 2, wherein the stretched edge materialtransmits along its length a force which is greater than the forceimparted to said material at the elastic limit of said material.
 4. Thepallet load of claim 1, wherein the edge material is of a differentmaterial than the material of the strands of the netting.
 5. The palletload of claim 4, wherein the edge material and the material of thestrands of the netting are both thermoplastic materials.
 6. The palletload of claim 5, wherein the edge material is stretched beyond itselastic limit under the tension forces applied to the netting to wrapthe pallet load.
 7. The pallet load of claim 6, wherein the stretchededge material transmits along its length a force which is greater thanthe force imparted to said material at the elastic limit of saidmaterial.
 8. The pallet load of claim 4, wherein the edge material isstretched beyond its elastic limit under the tension forces applied tothe netting to wrap the pallet load.
 9. The pallet load of claim 8,wherein the stretched edge material transmits along its length a forcewhich is greater than the force imparted to said material at the elasticlimit of said material.
 10. The pallet load of claim 1, wherein the edgematerial and strands of the netting are adhered together by a adhesive.11. The pallet load of claim 1, wherein the edge material and strands ofthe netting are simultaneously extruded and thereafter adhered together.12. The plastic netting of claim 1, wherein the edge material andstrands of the netting are adhered together by a adhesive.
 13. Theplastic netting of claim 1, wherein the edge material and strands of thenetting are simultaneously extruded and thereafter adhered together. 14.The pallet load of claim 1, wherein the edge material is stretched belowits elastic limit under the tension forces applied to the netting towrap the pallet load.
 15. A plastic netting for use in wrappingarticles, said netting having a longitudinally extending dimensionextending in a longitudinal direction and a transversely extendingdimension substantially perpendicular to said longitudinal direction andterminating at opposed longitudinally extending edges, said nettingincluding one set of spaced substantially parallel strands extending atan angle of less than 90 degrees upwardly with respect to thelongitudinal direction and a second set of spaced substantially parallelstrands overlying the first set and extending at an angle of less than90 degrees downwardly with respect to the longitudinal direction of thenetting length, said strands being joined at the intersections thereofand providing a diamond-like configuration to the netting, said nettingbeing biaxially oriented to preclude substantial stretching of thestrands thereof under tension forces applied in said longitudinaldirection to wrap articles with the netting, said one set of strands andsaid other set of strands being movable relative to each other under thetension forces applied in said longitudinal direction to permitelongation of the netting without substantial stretching of the strands,characterized in that an edge material extends along each longitudinaledge and is joined to both sets of strands, said edge material beingstretchable to a greater extent than the strands in both sets of strandsunder the tension forces applied to the netting to wrap the articles,said tension forces being transmitted along the stretched edge materialand the strands of the netting joined thereto so that substantially allof the netting strands, from one longitudinal edge to the otherlongitudinal edge in a direction substantially transverse to saidlongitudinal direction are maintained in a taut condition and undersufficient tension for immobilizing the wrapped articles.
 16. Theplastic netting of claim 15, wherein the edge material is stretchedbeyond its elastic limit under the tension forces applied to the nettingto wrap the articles.
 17. The plastic netting of claim 16, wherein thestretched edge material transmits along its length a force which isgreater than the force imparted to said material at the elastic limit ofsaid material.
 18. The plastic netting of claim 15, wherein the edgematerial is of a different material than the material of the strands ofthe netting.
 19. The plastic netting of claim 18, wherein the edgematerial and the material of the strands of the netting are boththermoplastic materials.
 20. The plastic netting of claim 17, whereinthe edge material is stretched beyond its elastic limit under thetension forces applied to the netting to wrap the articles.
 21. Theplastic netting of claim 20, wherein the stretched edge materialtransmits along its length a force which is greater than the forceimparted to said material at the elastic limit of said material.
 22. Theplastic netting of claim 18, wherein the edge material is stretchedbeyond its elastic limit under the tension forces applied to the nettingto wrap the articles.
 23. The plastic netting of claim 22, wherein thestretched edge material transmits along its length a force which isgreater than the force imparted to said material at the elastic limit ofsaid material.
 24. The plastic netting of claim 15, wherein the edgematerial is stretched below its elastic limit under the tension forcesapplied to the netting to wrap the articles.
 25. A biaxially orientedplastic netting for use in wrapping articles, said netting havingdiamond-shaped apertures formed by strands of the netting located at anacute angle to the longitudinal direction in which the web is tensionedfor wrapping articles, characterized in that said netting includes anedge material along each longitudinal edge thereof, said edge materialbeing stretchable to an elongation for permitting the strands in thelongitudinally extending central region to realign into a taut conditionwithout substantial stretching, said edge material, at said elongation,having sufficient resistance to increasing elongation to transmittension forces to the strands along the longitudinally extending edgesto render the strands adjacent each longitudinal edge taut under thetension forces imparted to the netting when it disposed in wrappingengagement with said articles to be wrapped.
 26. The plastic netting ofclaim 25, characterized in that the edge material is stretched beyondits elastic limit under the tension forces imparted to the netting whensaid netting is in wrapping engagement with the articles to be wrapped.27. The plastic netting of claim 26, characterized in that the tensionforce imparted to the strands through the edge material exceeds theforce imparted to the edge material at the elastic limit of said edgematerial.
 28. The plastic netting of claim 25, characterized in that theedge material is stretched below its elastic limit under the tensionforces imparted to the netting when said netting is in wrappingengagement with the articles to be wrapped.